@dipadp: Price depends on autogas system, tank size, injectors, reducer etc. Autogas consumption usually 12 to 20% more than petrol consumption. It's switch automatically to autogas when temperature of coolant is 30 degrees or another if we set different.
Characteristics of different controllers here : http://www.lpgain.com/index.php?option=com_content&view=category&layout=blog&id=40&Itemid=92